THEORIES OF INSTABILITY IN DENSE HIGHWAY TRAFFIC

It is shown' that the continuum theories and stable car-following theories are not capable of describing the spontaneous generation of stopp­ ages observed in the Holland Tunnel. An unstable car-following theory with a large reaction time has some desirable features but was abandoned because of mathematical difficulties. Most of the paper deals with a theory in which there are two velocity-headway curves one of whi~h applies during acceleration and the other during deceleration. Cars maintain larger spacings during acceleration. When the acceleration changes ~ign, cars make the transition from one curve to the other with only a small change in velocity. This theory furnishes possible explanations or descriptions of all phenomena observed so far on the gross aspects of traffic flow that are known to be in conflict with previous theories. Among other things the theory describes the existence of acceleration shocks, instability, stoppages behind a bottleneck and the variation of the flow-density curves with the nature of the flow pattern. A more complete summary of results is con­ tained in the concluding section.